Enjoyed your observations on the behaviors in the new aquarium. That is interesting about a female eating one (perhaps damaged or extra slow fry) and leaving the others alone. I've seem improbable assailants attack malformed fry. Though it sounds awful, maybe getting rid of those who would otherwise consume precious food but really can't contribute towards healthy descendants to keep the strain and species going.

Space may also strongly influence behavior. If the same number of guppies were in a 10-gallon, there might have been more cannibalism. As you suggested with that "let nature take its course" comment, as the population density in the 38 gets greater, less newborns may be tolerated.